1. Field of the Invention
The present invention relates to a zoom lens system which is mounted on a compact portable data handset, etc.
2. Description of the Prior Art
In recent years, a small digital camera module is provided in mobile phones and portable data handsets, e.g., a PDA (Personal Digital Assistants), etc. An optical system mounted on such a portable data handset has been increasingly required to attain further miniaturization and weight reduction. Currently, as the optical system mentioned above, there have been many optical systems in which (i) a single focal-length lens system is employed, and (ii) a digital-zooming function is provided so that the angle-of-view can be varied. Here, note that the digital-zooming function is to obtain a pseudo telephoto angle-of-view by trimming the periphery of the image plane. Moreover, as the optical system mentioned above, an optical zoom lens system (hereinafter, a zoom lens system) which has been made thinner in the optical axis direction has been proposed. As a specific example, a zoom lens system includes a first lens group having a negative refractive power (hereinafter, a negative first lens group) and a second lens group having a positive refractive power (hereinafter, a positive second lens group), in this order from the object. The angle-of-view is varied by changing the focal length thereof through the movement of the negative first lens group and the positive second lens group along the optical axis. Furthermore, there is a lens system in which a plurality of single focal-length lens systems are provided, and a single focal-length lens system is switched to another one in accordance with the desired magnification.
In the case where the zoom lens system of the two-lens-group arrangement mentioned above is employed in an apparatus such as a portable data handset which is required to be portable, operability of the apparatus is sacrificed since the lens groups are arranged to move in a forward direction or a backward direction along the optical axis upon zooming. If portability is more considered, an inner-zooming system would be preferable since no lens group is arranged to advance toward outside from an apparatus on which the zoom lens system is mounted.
On the other hand, in a lens system in which a single focal-length lens system out of a plurality of single focal-length lens systems is switched to another one in accordance with the desired magnification, spaces for storing the plural single focal-length lens systems have to be provided, and the manufacturing costs thereof increase; and still further, operability of the apparatus is sacrificed since a photographer has to change his/her posture every time the magnification is varied.